Synthesis and Optical Properties of [Cu6E6(SnPh)2(PPh2Et)6] (E = S, Se, Te) Cluster Molecules.

A homologous series of three copper-tin-chalcogenide cluster molecules [Cu6E6(SnPh)2(PPh2Et)6] (E = S, Se, Te) was synthesized by reactions of CuO(O)CCH3 and PhSnCl3 with E(SiMe3)2 in the presence of PPh2Et. The cluster cage structures are similar, with slight differences in the bridging modes of the respective chalcogenide ligands E. The onset of the optical absorption displays a significant decrease of ca. 1.1 eV on going from sulfur to tellurium. The differences in bonding and electronic excitations can be rationalized by DFT and TDDFT calculations. All complexes display near-infrared phosphorescence at cryogenic temperatures. In parallel with the absorption, the emission maximum shifts to lower energies in a series of sulfur, selenium, and tellurium compounds. In particular, the copper-tin-tellurium complex emits at an energy as low as ca. 0.97 eV (1280 nm).